A survey telescope reaches orbit
NASA's SPHEREx observatory launched from Vandenberg Space Force Base on 11 March 2025 and separated successfully into a Sun-synchronous orbit about 650 kilometres above Earth. Its name expands to Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer. The mission is designed to survey breadth rather than zoom in on a few targets: it will map the complete sky repeatedly in 102 infrared wavelength bands.
SPHEREx is about the size of a compact car, with a 20-centimetre telescope inside three nested cone-shaped photon shields. Those shields block heat and light from Earth and the Sun. Passive cooling keeps the detectors cold enough that the observatory's own infrared glow does not overwhelm faint celestial signals.
How 102-color mapping works
Instead of a moving spectrograph, SPHEREx uses six linear variable filters. Different positions on each filter transmit different wavelengths. As the spacecraft scans and the sky moves across the detector, the same location is recorded repeatedly through different portions of the filters. The result is low-resolution spectroscopy: more chemical and distance information than a broad-band image, collected across a much larger area than a narrow spectrograph could cover efficiently.
NASA plans roughly 600 exposures per day and four all-sky maps during the prime mission. The final survey is expected to include information on more than 450 million galaxies and over 100 million Milky Way stars. Its public archive will support research well beyond the mission's three headline goals.
Three connected science questions
First, SPHEREx will measure the three-dimensional distribution of galaxies over enormous volumes. Statistical patterns in that distribution can test models of cosmic inflation, the extremely rapid expansion thought to have occurred in the first fraction of a second after the Big Bang. The telescope will not image inflation itself; it will look for subtle large-scale signatures that different inflation models predict.
Second, the mission will estimate the total light produced by galaxies across cosmic history, including diffuse light from sources too faint or spread out to catalogue individually. Comparing that background with known galaxy populations can reveal how much star formation and black-hole growth standard surveys miss.
Third, infrared absorption features let SPHEREx identify water, carbon dioxide and other frozen compounds on interstellar dust grains. Mapping those ices through Milky Way clouds will show where ingredients associated with planets and life are stored before stars and planetary systems form. Detecting water ice is chemistry, not evidence of life.
What this telescope will not replace
SPHEREx trades fine spatial and spectral detail for uniform coverage. Webb can obtain far deeper, higher-resolution spectra of selected objects, while large ground-based telescopes can resolve individual galaxies in greater detail. SPHEREx supplies the catalogue and statistical context: it can identify unusual regions, populations and targets for those observatories to examine.
Launch success also did not equal immediate scientific success. After separation, the spacecraft needed checkout, cooling, calibration and removal of its protective dust cover before routine surveying. Its cosmology analyses require careful control of instrument response, foreground stars, Galactic dust and biases in estimating galaxy distances.
Why an all-sky spectral archive matters
A repeated, consistently calibrated survey lets researchers compare the same wavelengths in every direction and search for changes over time. That uniformity is difficult to assemble from unrelated observing programmes. Because NASA is releasing the data publicly, future teams can ask questions the original mission designers did not anticipate and combine the maps with Euclid, Rubin, Webb and radio surveys.
SPHEREx therefore fills a distinct role in modern astronomy. Its small telescope will not make the deepest single image, but its 102-color view turns the entire sky into a shared spectral dataset for cosmology, galaxy evolution and the chemistry of star-forming clouds.
